The present invention relates to an exposure counter disc mechanism for a camera which is constructed to gain exposure count information directly from the rotation of a sprocket at the time of film windup, and to a camera back cover construction including the same.
Prior exposure counter disc mechanisms are known which obtain exposure count information via a roller from a sprocket and a shaft rotatable upon film windup, the roller being rotatable by friction with the film. When the film is fed at a high rate as by a motor drive, the roller and the film tend to slip with respect to each other causing over-lapped exposure frames and a discrepancy between the number of film frames acutally fed and the indication on the exposure counter. Such an exposure counter disc mechanism can count up to a maximum of 36 consecutive film frames. When a camera equipped with such an exposure counter disc mechanism is loaded with a film of more than 36 frames such as a film having 72 frames, up to 36 frames can be counted and the rest cannot. Films having more than 36 frames such as 72-frame films are composed of thinner film bases as they are placed in conventional cartridges for 36-frame films. Rails in the camera which are constructed for use with 36-frame films fail to allow such thinner-base films to fit snugly in the film passage, with the result that the film tends to slacken. Image focusing on the film is adversely effected by such film slackening.